A clot removal device

ABSTRACT

A clot retrieval system comprises a clot retrieval device, a catheter  51 , and a tubular shield element  61 . The clot retrieval device comprises an elongate member  53  having a proximal end and a distal end, and a clot engaging element  54  at the distal end of the elongate member  53  the clot engaging element  54  having a collapsed delivery configuration and an expanded deployed configuration. The catheter is adapted for placement at a location at which a distal end of the catheter is proximal of the clot engaging element and the tubular shield element  61  extends over the elongate member  53  and is adapted for location between the distal end of the catheter and the proximal end of the clot engaging element  54 . The tubular shield element  61  is movable relative to the elongate member  54  when the clot engaging element is in the expanded configuration in that the force that is applied on retraction of the elongate member is spread over the outer surface of the tubular shield element. The force that would usually be exerted on vessels on retrieval of the clot engaging element is spread by the shield element thus reducing the effects of abrasion.

FIELD OF THE INVENTION

This invention relates to endovascular medical devices which areretracted through a portion of the vasculature while in contact with thevessel wall as part of their typical method of use. In particular thisinvention is of benefit to mechanical thrombectomy devices, vena cavafilters, embolic filters, stents and similar devices. For example, it isrelevant to clot retrieval devices which are used to retrieve bloodclots in the case of ischemic stroke, or in another example, stentswhich are used to relieve stenosis.

BACKGROUND

Mechanical thrombectomy devices such as clot retrieval devices orstentrievers are frequently used to recanalize blocked cerebral arteriesin patients suffering from acute ischemic stroke. The method of use ofsuch a device typically involves positioning a large diameter catheterin a location proximal of the obstructive clot, and then advancing amicrocatheter and guidewire together to a location distal of the clot.The guidewire is then withdrawn proximally to allow for the introductionof the clot retrieval device in the collapsed configuration through themicrocatheter. A generic clot retrieval device is comprised of anelongate member and a clot engaging body connected to the distal end ofthe elongate member. The clot retrieval device is advanced distallywithin the microcatheter until is it situated within the clot. At thisstage the microcatheter is withdrawn and the device will expand. As thedevice expands it engages and captures the clot. Once the clot has beencaptured by the engaging body of the device, aspiration is typicallycarried out through the large diameter catheter while the device and theclot are withdrawn towards the large diameter catheter (which may be aguide catheter or a sheath or a distal access catheter). The device andthe clot are withdrawn into the large diameter catheter and removed fromthe vasculature.

The force required to retract the device may have undesiredconsequences. In order to dislodge the clot from the vessel a force mustbe applied to it through the stentriever device. This force iseffectively applied to the vessel in which the clot is lodged and to thedistal vascular bed, placing these vessels in tension and placing thevessels proximal of the clot in compression. Once the clot begins tomove there is relative movement between the stentriever device and shaftand the vessel wall. This relative movement can cause abrasion anddamage to the endothelia and underlying layers of the vessel wall, whichmay result in a dissection or perforation, or could give rise to thesubsequent formation of thrombus which could then be liberated to createan additional stroke.

The force that must be applied to dislodge and retract the clot isdependent not only on how well lodged the clot is in the vessel, butalso on the frictional losses that occur where the stentriever devicecontacts vessel walls or the inner surface of the catheter through whichit passes. Thus it would be advantageous to have the use of a devicewhich acts as a shield between the elongate shaft and the vessel wall.In the preferred embodiment the invention would remain in situ in thevessel as the elongate shaft is being retracted and absorb the tensionwhich would normally be exerted on the shaft and the vessels. Preferablythe invention would have a low friction inner surface and a higherfriction outer surface. This would allow the shaft to move more fluidlywithin the device while the device remained in the vessel. The presentinvention includes these features and improves upon the methods of clotretrieval previously discussed.

SUMMARY OF THE INVENTION

According to the invention there is provided a clot retrieval systemcomprising:—

-   -   a clot retrieval device;    -   a catheter; and    -   a tubular shield element    -   the clot retrieval device comprising an elongate member having a        proximal end and a distal end, and a clot engaging element at        the distal end of the elongate member the clot engaging element        having a collapsed delivery configuration and an expanded        deployed configuration,    -   the catheter being adapted for placement at a location at which        a distal end of the catheter is proximal of the clot engaging        element,    -   the tubular shield element extending over the elongate member        and being adapted for location between the distal end of the        catheter and the proximal end of the clot engaging element and        being movable relative to the elongate member when the clot        engaging element is in the expanded configuration.

The force that would usually be exerted on vessels on retrieval of theclot engaging element is spread by the shield element thus reducing theeffects of abrasion.

In use, there is a gap between the distal end of the catheter and theproximal end of the clot engaging element. The tubular shield elementmay extend partially across this gap or in some cases fully across thegap. In some cases the shield element extends partially into the distalend of the catheter.

In one embodiment the tubular shield element is slidable relative to theelongate member.

In one case the elongate member comprises a distal stop and a proximalstop to limit the sliding movement of the tubular element.

In one embodiment the tubular shield element comprises a distal abutmentsurface and a proximal abutment surface.

In one case the tubular shield element comprises an inner lumen and anouter surface, the inner lumen being sized to slide freely over at leasta distal portion of the elongate member.

In one embodiment the tubular shield element inner lumen comprises afirst material and the tubular element outer surface comprises a secondmaterial.

In one case the tubular shield element first material comprises a lowercoefficient of friction than the tubular element second material.

In one embodiment the system further comprises a microcatheter fordelivery of the clot engaging element in the collapsed configuration.

In one case the lumen of the microcatheter is configured to receive thetubular shield element. The outer diameter of the tubular element may beat least as small as the diameter of the clot engagement element in itscollapsed configuration.

The disclosed designs overcome the disadvantages of existing mechanicalthrombectomy solutions.

In one embodiment a tubular member is slidably disposed on the shaft ofa thrombectomy device.

The device captures the clot in the engaging body. Once the clot hasbeen captured the device is withdrawn proximally through thevasculature. The withdrawal of the device places pressure on thesurrounding vessels and causes abrasion on the inner walls of thevessels. This is the stage at which the highest loads are applied.However the use of a slider tube reduces these forces. As it is slidablydisposed on the elongate shaft of the thrombectomy device and thecoefficient of friction between the tube and elongate shaft is lowerthan that between the slider tube and the vessel, the slider tuberemains in situ as the shaft is retracted. The force that the elongateshaft would normally exert on the vessels is spread over the outersurface area of the tube. Therefore there is less friction within thevessels and this reduces the effects of abrasion.

The device reduces the friction within the vessel and it also reducesthe overall force required to withdraw the elongate shaft. As the levelof friction is reduced the forces of compression on the surroundingvasculature are consequently reduced. The slider tube may contain lowdiameter regions and/or highly flexible regions as described below andthese regions increase the flexibility of the tube and thus furtherreduce the forces on the neighbouring vascular bed. Therefore theoverall force required to remove the clot is reduced, which in turnreduces the forces on the vascular bed. Therefore the key benefit of thepresent invention is a significant reduction in rubbing of the elongateshaft against vessel walls during the initial dislodgement andrefraction of the clot.

The slider tube is preferably of an outer diameter that fits within thelumen of a low profile microcatheter, as this enables the safest andeasiest crossing of the obstructive clot during initial access. Typicalmicrocatheters used in this kind of procedure range from an inner lumensize of approximately 0.016″ to 0.027″, and have a distal end outerdiameter of between approximately 0.020″ to 0.039″. Preferred lowerprofile microcatheters have a lumen of approximately 0.021″ or less andhave a distal end outer diameter of approximately 0.033″ or less. Theslider tube outer diameter is preferably the largest diameter than canmove freely through the microcatheter lumen, as a larger diameter slidertube will have a lower vessel wall contact pressure for a given force(and hence be less traumatic to the vessel wall) than would a smallerdiameter slider tube. Thus the slider tube outer diameter could be inthe range of 0.010″ to 0.026″, but is preferably at least 0.012″ and notmore than 0.020″, and is most preferably in the range of 0.014″ to0.019″.

An additional benefit of the present invention is the prevention ofaccidental retraction of the clot retrieval device into the distal endof the microcatheter and subsequent loss of the clot. This could occurshould a physician attempt to use the microcatheter in the manner of aslider tube, namely withdraw the clot retrieval device as far as themicrocatheter and withdraw the microcatheter a little further and soforth. This increases the possibility of the device being withdrawn intothe microcatheter and resuming its collapsed configuration and thereforelosing control of the clot. If a slider tube is used the microcatheteris withdrawn a significant distance and the slider tube willautomatically start to advance proximally with the device once thedistal end of the slider tube contacts the shaft. The process functionsthus as there is less energy expended as the device shaft slides throughthe slider tube compared to the slider tube moving through the vessel.This effect is influenced by the difference in the coefficient offriction between the slider tube and shaft and between the slider tubeand vessel, and also by the relative lateral stifihesses of shaft andslider tube.

One embodiment of this invention comprises a system for dislodging anocclusive clot from a first blood vessel segment the system comprising:a clot retrieval device and a clot removal catheter, the clot retrievaldevice comprising a clot engaging element and an elongate member, theclot engagement element having a collapsed delivery configuration and anexpanded configuration for engaging with the clot and for dislodging theclot from the first vessel segment, the elongate member configured toapply a pull force to the clot engaging element to dislodge the clotfrom the first vessel segment, the clot removal catheter comprising alumen at its distal end sized to receive said clot and configured tomaintain a stable position in a second blood vessel segment, said secondblood vessel segment being proximal of and larger in diameter than saidfirst blood vessel segment, a third blood vessel segment between saidfirst and second blood vessel segments, the distal end of the elongatemember configured to protect the third blood vessel segment fromtractive forces transmitted by the elongate member during clotdislodgement from the first vessel segment.

The system may further comprise an elongate structural element and aslider tube, the slider tube configured to slide relative to theelongate structural element.

In one case the elongate member is configured so that the slider tubeslides over a distal section of the elongate structural element.

In one embodiment the slider tube comprises a proximal position and adistal position.

In one case the slider tube can slide freely over the surface of theelongate member between a proximal position and a distal position.

In one embodiment the clot retrieval device is delivered to theocclusion site in the first vessel segment through a catheter and theadvancement of the clot retrieval device through the lumen of thedelivery catheter biases the slider tube in a proximal position.

In one case the slider tube comprises an inner lumen and an outersurface and the inner lumen is sized to slide freely over at least thesurface of a distal portion of the elongate structural element.

In one embodiment the slider tube inner lumen comprises a first materialand the slider tube outer surface comprises a second material.

In one case the slider tube first material comprises a lower coefficientof friction than the slider tube second material.

In one embodiment the slider tube comprises a distal abutment surfaceand a proximal abutment surface.

In one case the elongate structural element comprises a distal stop anda proximal stop to limit the sliding movement of the slider tube.

In one embodiment the proximal stop and/or the distal stop of theelongate structural element comprise an abutment surface, a collar, atube end, a spring end, a tether, a tapered shaft section, a diameterchange, or a surface projection.

In one case the elongate member is at least partially a nitinol materialor a stainless steel material.

In one embodiment a distal end of the elongate member is connected tothe clot engaging element and the proximal end of the elongate memberextends exterior of the patient.

In one case the slider tube encircles the elongate structural elementover at least a distal portion of its length.

In one embodiment the tractive forces acting on the third blood vesselsegment comprise a combination of normal forces acting on the vesselwall and tangential forces acting along the third blood vessel segmentwall.

In one case the tractive forces acting on the third blood vessel segmentcomprise dynamic forces associated with relative movement between thethird segment vessel wall and the elongate member.

In one embodiment the elongate member comprises an elongate structuralelement and a slider tube the slider tube configured to allow relativemovement between the elongate structural element and the slider tubeduring clot dislodgement.

In one case the system comprises a microcatheter for delivering the clotremoval device to the occlusive clot in the first vessel segment, themicrocatheter comprising a lumen sized to receive the clot engagementelement in its collapsed configuration.

In one embodiment retraction of the microcatheter effects deployment ofthe clot engagement element.

In one case the microcatheter lumen is configured to slidably receivethe slider tube.

In one embodiment the slider tube outer diameter is at least as small asthe diameter of the clot engagement element in its collapsedconfiguration.

Another embodiment of this invention comprises a clot removal device forremoving an occlusive clot form a distal blood vessel of a patient, theclot removal device comprising a clot engaging element, an elongatemember and a tractive tubular member, the clot engagement element havinga collapsed delivery configuration and an expanded configuration forengaging with the occlusive clot and for dislodging the occlusive clotfrom the distal blood vessel, the elongate member comprising a proximalsection, an intermediate section and a distal section, a distal end ofthe distal section of the elongate member connected to the clot engagingelement and the proximal end of the elongate member extending exteriorof the patient, the elongate member further configured to transmit apull force applied by the user to the clot engaging element to dislodgethe clot from the distal blood vessel, the tractive tubular memberconfigured to encircle the elongate member over at least a portion ofthe length of the elongate member distal section, the distal section ofthe elongate member being slidable and rotatable relative to thetractive tubular member, the elongate member distal section and thetractive tubular member configured to protect the proximal blood vesselfrom tractive forces transmitted by the elongate member during clotdislodgement from the distal vessel segment.

In one embodiment the tractive tubular member is slidable between aproximal position and a distal position along the distal section of theelongate member.

In one case the tractive tubular member comprises an inner lumen and anouter surface and a proximal abutment surface and a distal abutmentsurface.

In one embodiment the interface between the elongate member distal endand the tractive tubular member comprises the outer surface of thedistal section of the elongate member and the inner surface of the lumenof the tractive tubular member.

In one case the interface between the elongate member distal section andthe tractive tubular member is configured to facilitate low frictionsliding of the tractive tubular member relative to the elongate member.

In one embodiment the coefficient of friction of the inner surface ofthe tractive tubular member is less than the coefficient of friction ofthe outer surface of the tractive tubular member.

The distal section of the elongate member may comprise a polishedsurface or a buffed surface.

In one case the distal section of the elongate member comprises alongitudinally polished surface or a longitudinally buffed surface

In one embodiment the clot removal device is delivered to the occlusionsite in the distal blood vessel through a catheter and the advancementof the clot removal device through the lumen of the catheter biases thetractive tubular member towards the proximal end of the elongate memberdistal section.

In one case the tractive tubular member inner surface comprises a firstmaterial and the tractive tubular member outer surface comprises asecond material.

In one embodiment the tractive tubular member first material comprises alower coefficient of friction than the tractive tubular member secondmaterial.

In one case the elongate member comprises a distal stop and a proximalstop, said distal and proximal stops configured to limit the distance ofsliding of the tractive tubular member.

In one embodiment the proximal stop and/or the distal stop of theelongate member comprise an abutment surface, a collar, a tube end, aspring end, a tether, a tapered shaft section, a diameter change, or asurface projection.

In one case the elongate member is at least partially a nitinol materialor a stainless steel material.

In one embodiment the slider tube encircles the elongate member distalsection over at least a portion of its length.

In one case the clot removal device comprises a sliding distance, saidsliding distance comprising the distance along the elongate member thatthe tractive tubular element can slide without obstruction.

The sliding distance may be at least as long as the length of theocclusive clot, in some cases the sliding distance is at least 10 mm,the sliding distance is at least 20 mm, wherein the sliding distance isat least 30 mm, wherein the sliding distance is at least 40 mm, whereinthe sliding distance is at least 50 mm, or the sliding distance is lessthan 150 mm.

In one embodiment the tractive forces acting on the proximal bloodvessel comprise a combination of normal forces acting on the vessel walland tangential forces acting along the proximal blood vessel wall.

In one case the tractive forces acting on the proximal blood vesselcomprise dynamic forces associated with relative movement between theproximal blood vessel wall and the elongate member.

In one embodiment the clot removal device comprises a microcatheter fordelivering the clot removal device to the occlusive clot, themicrocatheter comprising a lumen sized to receive the clot engagementelement in its collapsed configuration.

In one case retraction of the microcatheter effects deployment of theclot engagement element.

In one embodiment the microcatheter lumen is configured to slidablyreceive the tractive tubular member.

In one case the tractive tubular member outer diameter is at least assmall as the diameter of the clot engagement element in its collapsedconfiguration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingexamples.

FIG. 1 a shows a conventional method for removing a clot;

FIG. 1 b shows the forces and abrasion on vessels during retraction ofclot;

FIG. 2 is a detailed illustration of the clot retrieval system of thepresent invention;

FIG. 3 a shows a novel method for clot retrieval;

FIG. 3 b shows the retrieval of clot using the present invention;

FIG. 4 shows alternative embodiments of the present invention withstops;

FIG. 5 shows alternative embodiments of the present invention with aspring;

FIG. 6 shows alternative embodiments of the present invention with atether;

FIG. 7 shows an isometric view of an alternative embodiment of thepresent invention with stiff and rigid sections;

FIG. 8 a shows alternative embodiments of the present invention withflexible sections;

FIG. 8 b shows detail of the device of FIG. 8 a in isometric view;

FIG. 9 shows alternative embodiments of the present invention withsections of varying friction;

FIG. 10 shows alternative embodiments of the present invention withsections of varying diameter;

FIG. 11 a shows the method of use of the clot retrieval system of thepresent invention;

FIG. 11 b illustrates a microcatheter being advanced in a vessel;

FIG. 11 c illustrates the clot retrieval device expanding within a clot;

FIG. 11 d illustrates the microcatheter being retracted and the slidertube being deployed;

FIG. 11 e illustrates the clot retrieval device being stopped by thedistal mechanical stop and the slider tube; and

FIG. 11 f illustrates the slider tube and the clot retrieval device andthe clot being retracted.

DETAILED DESCRIPTION

Specific embodiments of the present invention are now described indetail with reference to the figures, wherein identical referencenumbers indicate identical or functionality similar elements. The terms“distal” or “proximal” are used in the following description withrespect to a position or direction relative to the treating physician.“Distal” or “distally” are a position distant from or in a directionaway from the physician. “Proximal” or “proximally” or “proximate” are aposition near or in a direction toward the physician. The invention isapplicable to any mechanical thrombectomy clot retrieval device, and ageneric design of such a clot retrieval device is shown in theillustrations.

FIG. 1 a-b shows the conventional method of retrieving a clot from atortuous vasculature. A guidewire and microcatheter 7 are inserted intothe artery and are advanced across the occlusive clot 5, which is lodgedat a bifurcation using any conventionally know techniques.

The guidewire is removed from the microcatheter 7 to allow the clotretrieval device 1 to be advanced in a collapsed configuration until itis located within the clot 5. The device 1 is deployed on retraction ofthe microcatheter 7. The device comprises an elongate shaft 3, havingthe distal end that extends interior of the artery and a proximal endthat extends exterior of the artery. It has a clot engaging body 4 whichis connected to the distal section of the elongate element 3. Onexpansion, the device exerts a radial force upon the clot and capturesthe clot against the lumen of the vessel 2.

Once the clot retrieval device has captured the clot, the device isretracted proximally. The force which is pulling the device proximallyalso exerts a force 9 on the vessels in the immediate vicinity 8 thuspulling these vessels towards the microcatheter 7 and potentiallydistorting the vasculature in the area as illustrated in FIG. 1 b.Furthermore, the proximal force on the device also distorts the vessel 2in which the elongate member 3 is being retracted. The force compels thevessel 2 to conform to the shape of the elongate member thus forcing itto straighten and lose its original shape. It compresses the vessels inthe immediate vicinity of the elongate member 3. In addition, theelongate member 3 may cause abrasion 10 within the lumen of the vessel 2as it is retracted. As the vessel 2 distorts the elongate member 3 isforced to contact the walls of the vessel which may cause the vessel tolose or damage the endothelia of the vessel at these points.

The vessel distortion and abrasion could be avoided by leaving themicrocatheter 7 more distal (and closer to the clot retrieval device)when initially retracting the clot retrieval device, however this couldeasily result in the user retracting the clot retrieval device, thuscollapsing the device within the microcatheter 7 and liberating theclot.

FIG. 2 is a detailed illustration of a clot retrieval device of thepresent invention. The slider tube design described in FIG. 2 avoidsvessel damage without the risk of inadvertent device retraction into themicrocatheter. The device 51 has an elongate shaft 53 having a distalend that extends interior of the artery and a proximal end that extendsexterior of the artery, a clot engaging body 54 configured at the distalend of the elongate shaft, tethers 52 having distal ends connected tothe proximal end of the clot engaging body 54 and proximal endsconnected to the elongate element 53. A coil 66 is slidably disposedaround the elongate member 53, the distal end of which is locatedproximal of a distal stop 63 and the proximal end is located within thelumen of a slider tube 61. The tubular member 61 is slidably disposedaround the elongate shaft 53. The distal end of the slider tube 61extends over the coil 66 and the proximal end is located distal of theproximal stop 64. The slider tube itself may comprise a range ofconstructions, some of which are shown in FIGS. 4 to 10. The slider tube61 is preferably a solid tube composed of flexible material such that itmay be retracted through tortuous vasculature without deforming it. Inone preferred embodiment the slider tube 61 is composed of a polymersuch as PEN, PET, UHMWPE, LCP or Aramid.

In a preferred embodiment the elongate member 53 has a lower coefficientof friction while being retracted through the slider tube 61 whencompared to that between the slider tube and the vessel. As a result,the slider tube 61 remains in situ as the elongate shaft 53 is retractedand during dislodgment of the clot thereby protecting the walls of thevessel from abrasion.

The overall effect of the slider tube 61 is to spread the pressure andtension that the elongate member 53 normally exerts on the vessel acrossthe entire surface area of the tube 61 thus reducing the tension fromaccumulating in any one particular area in the vessel.

In addition, the use of a slider tube 61 is a more secure form ofprevention of abrasion than a microcatheter. If the microcatheter wasused in an effort to prevent abrasion of the inner walls of the vesselthe device may potentially re-enter the microcatheter. If this occurredthe device would compress into its collapsed configuration and it maylose control of the clot. The clot would then be free to travel to themore distal vasculature and occlude a smaller vessel with potentiallycatastrophic consequences. As the distal stop 63 and the slider tube 61are located between the device 51 and the microcatheter this occurrenceis prevented.

FIG. 3 a-b illustrates the preferred method of retrieving a clot fromtortuous vasculature using the present invention. A guidewire 103 andmicrocatheter 107 are inserted into the artery and are advanced acrossthe occlusive clot 105, which is lodged at a bifurcation using anyconventionally know techniques. The guidewire 103 is removed from themicrocatheter to allow the clot retrieval device 101 to be advancedwithin the microcatheter in a collapsed configuration until it islocated within the clot. The device 101 is deployed on retraction of themicrocatheter 107. The device has an elongate shaft 103, having a distalend that extends interior of the artery and a proximal end that extendsexterior of the artery. On expansion, the device exerts a radial forceupon the clot 105 and captures the clot against the lumen of the vessel102.

On further retraction of the microcatheter 107, the distal stop 113 isdeployed. This is followed by the deployment of a slider tube 111 and adistal stop. The distal and proximal stops are connected to the elongatemember 103 at the distal and proximal ends of the slider tube 111. Thetubular member 111 is slidably disposed along the elongate member 103.Upon the deployment of the slider tube 111, the clot retrieval device101 is then retracted proximally by means of the elongate member 103.The device 101 is retracted until the distal stop reaches the distal endof the slider tube 111. When it reaches the slider tube 111, the slidertube 111 is automatically withdrawn as the clot retrieval device 101 andthe clot 105 are withdrawn proximally into the guidecatheter 106.

FIG. 4 a illustrates another alternative embodiment of the presentinvention. The device 151 in this case having distal end that extendsinterior of the artery and a proximal end that extends exterior of theartery, a clot engaging body 154 and control tethers 165. The distalends of the control tethers are attached to the proximal end of theengaging body 154 and the proximal ends are attached to the distal endof the elongate member 153.

The slider tube 161 is slidably disposed around the elongate member 153.The distal stop 163 is affixed to the distal end of the elongate member153. The proximal stop 164 is affixed to the elongate member proximal ofthe slider tube 161. The slider tube 161 is held in place by the distal163 stop and the proximal stop 164. The device 151 is advanced throughthe microcatheter in a collapsed configuration until it is within theclot. Once the device is deployed it expands and captures the clot byexerting a radial pressure on the clot. As the device is beingretracted, the slider tube 161 is automatically withdrawn as the clotretrieval device 151 is withdrawn proximally into the guidecatheter.

FIG. 5 illustrates another alternative embodiment of the presentinvention. The device 201 having a distal end that extends interior ofthe artery and a proximal end that extends exterior of the artery, aclot engaging body 204 and control tethers 215. The distal ends of thecontrol tethers 215 are attached to the proximal end of the engagingbody 204 and the proximal ends are attached to the distal end of theelongate member 203. A slider tube 211 contains the elongate member 203at the distal end of the elongate member 203. The device contains aspring 218 having distal ends attached to the distal end of the elongatemember 203 and proximal end attached to the elongate shaft distal. Inthis embodiment of the invention, there is no requirement for a distalstop as the spring 218 functions as a distal stop. As the clot retrievaldevice is retracted the slider tube 211 automatically begins to withdrawas soon as the proximal end of the spring 218 contacts the distal end ofthe slider tube 211.

In the preferred embodiment the spring 218 is a soft spring andtherefore the spring 218 also has the effect of reducing the tensionbetween the device 201 and the elongate member 203 and the slider tube211 during retraction of the device 201. The proximal stop 213, which islocated at the proximal end of the slider tube 211, prevents the slidertube 211 from retracting further into the microcatheter upon deployment.

FIG. 6 illustrates another alternative embodiment of the presentinvention. A clot retrieval device 251 has a distal end that extendsinterior of the artery and a proximal end that extends exterior of theartery, a clot engaging body 254 and control tethers 265. The distalends of the control tethers 265 are attached to the proximal end of theengaging body 254 and the proximal ends are attached to the distal endof the elongate member 253. A slider tube 261 is slidably disposedaround the elongate member 253 at the distal end of the elongate member253. A distal stop 263 is located at the distal end of the elongatemember 253. An elongate tether 269, having distal end affixed to thedistal end of the elongate member 253 and proximal of the distal stopand proximal end attached to the slider tube 261, has the effect oftying the slider tube 261 to the device while allowing it to move withinthe vasculature thus reducing the overall friction of the device duringretraction. The elongate tether 269 functions as a proximal stop for theslider tube.

FIG. 7 is an isometric view of a section of an alternative embodiment ofthis invention. A slider tube 311 comprises an atraumatic design whereinalternative sections of the tube are composed of regions of stiffmaterial 312, which are punctuated by flexible joint regions orarticulation regions 313. This design allows the tube to articulate withthe vasculature without distorting the vessels or causing abrasion tothe walls of the vessels. The slider tube 311 is slidably disposedaround the elongate member and contains the elongate member duringretraction and prevents it from causing abrasion or distorting thevessels. This embodiment also reduces the compression of the vesselsproximal of the device. Any number of flexible joints and stiff regionscan be used at any section along the tube and can be used in conjunctionwith any tubular device disclosed elsewhere in this document.

FIG. 8 a is an isometric view of a section of an alternative embodimentof the present invention. A slider tube 361 comprises an atraumaticdesign wherein the tube is punctuated by flexible regions 362 alternatedwith rigid regions 363. The flexible regions 362 are composed ofsections of tubing in which sections of the tubing have been removed.These slits 364 allow the slider tube to be more flexible as it reducesthe outer surface area of the tube and allows it bend at smaller angles.During retraction this reduces the effect of abrasion of the vessels andprevents distortion and compression of the vessels proximal of thedevice thus enhancing the device performance. FIG. 8 b is an isometricview of the slits 414 in the slider tube 411. The slits may be of anyshape and size and number and they may be located at any section acrossthe tube. Such slits may be used in conjunction with any other tubulardesigns disclosed elsewhere in this document.

FIG. 9 is an isometric view of a section of an alternative embodiment ofthe present invention. A slider tube 461 is comprised of an atraumaticdesign wherein the tube is comprised of alternating low friction regions462 and high friction regions 463. The low friction regions may becreated by electropolishing the tube to obtain a smooth outer surfaceand the high friction regions may be created by fashioning slightprotrusions which emanate from the outer surface of the tube. Theprotrusions may be of any shape or size or number. In the preferredembodiment the effect of the varying regions of high and low frictionwould be to spread the pressure and tension that the elongate memberexerts on the vessel across the entire surface area of the tube thusreducing the tension from accumulating in any one particular area in thevessel. The slight increase in friction of these alternating regionswill increase the efficiency of the elongate element as it moves throughthe slider tube. This effect is due to the higher coefficient offriction between the slider tube and the vessel compared to the lowercoefficient between the elongate element and the slider tube. The resultis that the slider tube remains in situ as the elongate shaft isretracted thus protecting the vessel walls from abrasion. Any number oflow friction regions and high friction regions can be used at anysection along the tube and can be used in conjunction with any tubulardevice disclosed elsewhere in this document.

FIG. 10 is an isometric view of a section of an alternative embodimentof the present invention wherein a slider tube 511 is composed ofregions of small 512 and large diameter 513. The regions of smalldiameter 512 may alternate with regions of large diameter 513 thuscreating a low profile device. The atraumatic design reduces the forceand tension on the vasculature as it increases the flexibility of thetubular device and it decreases the risk of abrasion. In the preferredembodiment the effect of the varying regions of smaller and largerdiameter would be to spread the pressure and tension that the elongatemember exerts on the vessel across the entire surface area of the tubethus reducing the tension from accumulating in any one particular areain the vessel. Any number of small diameter regions and large diameterregions can be used at any section along the tube and can be used inconjunction with any tubular device disclosed elsewhere in thisdocument.

Use of a slider tube of the present invention in conjunction with a clotretrieval device of the present invention in removing an obstructiveclot 555 from an intracranial artery 552 is depicted in FIG. 11 a-f. Aguidewire 566 and microcatheter 557 are inserted in the artery 552 bymeans of a guidecatheter 556 and are advanced across an obstructive clot555 using any conventionally known techniques. The guidewire 566 isremoved from the microcatheter 557 to allow the clot retrieval device551 and the slider tube 561 to be advanced through the microcatheter inthe collapsed configuration until the clot retrieval device 551 iswithin the clot 555. The device has an elongate shaft 553, having adistal end that extends interior of the artery and a proximal end thatextends exterior of the artery, distal stop 563 which is located at theproximal end of the ring elements and proximal stop 564 which is locatedat the proximal end of the slider tube 561. It has a clot engaging body554 which is connected to the elongate element 553.

The microcatheter 557 is retracted to deploy the clot retrieval device551 within the clot in a manner that the engaging portion of the clotretrieval device is positioned across the clot. The engaging section ofthe clot exerts a gentle radial force on the clot while maintaining theintegrity of the clot and avoiding its dissection. The microcatheter 557is then further retracted proximally to deploy the mechanical stops 563and 564 and the slider tube 561 within the vessel 552. Once the clotretrieval device 551 has engaged the clot 555 the device 551 isretracted proximally by means of the elongate 30 member 553 to which thedevice is affixed. The device is retraced proximally until the distalstop 563 makes contact with the slider tube 561. When the distal stop563 has contacted the slider tube 561, the slider tube 561 willautomatically be withdrawn as the device 551 and the microcatheter 557are withdrawn proximally into the distal end of the guidecatheter 556.

During this process the tension and the force that the elongate element553 would normally exert on the inner lining of the vessel is absorbedby the slider tube 561 and spread across the entre outer surface of theslider tube 561. Therefore the slider tube prevents excessive distortionof the vessel and prevents abrasion of the inner walls of the vessel.

Furthermore, the slider tube 561 is a more secure form of prevention ofabrasion when compared to a microcatheter 557. If the microcatheter 557was used in the manner of a slider tube 561, the device 551 mayunintentionally withdraw into the microcatheter. Should this happen thedevice 551 would compress into its collapsed configuration and the clot555 would escape from the device and leaving open the possibility thatit might advance distally through the vessel and occlude a smallervessel at another junction in the vasculature. As the slider tube 561and the mechanical stops 563 and 564 are located between the device 551and the microcatheter 557 this reduces the possibility of thisoccurring.

The slider tube 561 may be comprised of slits or rigid and flexibleregions and/or high and low friction regions or any combination of theabove as disclosed elsewhere in this document. It may be attached to theelongate member by the means described previously such as by a tether ora spring. It may also be held in situ around the elongate member byproximal and/or distal stops. Preferably the slider tube 561 is composedof a polymer such as PEN, PET, UHMWPE, LCP or Aramid. The slider tube561 may be used in conjunction with any mechanical thrombectomy devicesuch as Stentrievers.

Modification and additions can be made to the embodiments of theinvention described herein without departing from the scope of theinvention. For example, while the embodiments described herein refer toparticular features, the invention includes embodiments having differentcombinations of features. The invention also includes embodiments thatdo not include all of the specific features described.

The invention is not limited to the embodiments hereinbefore describedwhich may be varied in construction and detail.

1. A clot retrieval system comprising: a clot retrieval device; acatheter; and a tubular shield element the clot retrieval devicecomprising an elongate member having a proximal end and a distal end,and a clot engaging element at the distal end of the elongate member theclot engaging element having a collapsed delivery configuration and anexpanded deployed configuration, the catheter being adapted forplacement at a location at which a distal end of the catheter isproximal of the clot engaging element, the tubular shield elementextending over the elongate member and being adapted for locationbetween the distal end of the catheter and the proximal end of the clotengaging element and being movable relative to the elongate member whenthe clot engaging element is in the expanded configuration so that aretraction force applied to the elongate member is spread over the outersurface of the tubular member.
 2. A clot retrieval system as claimed inclaim 1 wherein the tubular shield element is slidable relative to theelongate member.
 3. A clot retrieval system as claimed in claim 2wherein the elongate member comprises a distal stop and a proximal stopto limit the sliding movement of the tubular element.
 4. A clotretrieval system as claimed in claim 2 wherein the tubular shieldelement comprises a distal abutment surface and a proximal abutmentsurface.
 5. A clot retrieval system as claimed in claim 1 wherein thetubular shield element comprises an inner lumen and an outer surface,the inner lumen being sized to slide freely over at least a distalportion of the elongate member.
 6. A clot retrieval system as claimed inclaim 1 wherein the tubular shield element inner lumen comprises a firstmaterial and the tubular element outer surface comprises a secondmaterial.
 7. A clot retrieval system as claimed in claim 6 wherein thetubular shield element first material comprises a lower coefficient offriction than the tubular element second material.
 8. A clot retrievalsystem as claimed claim 1 further comprising a microcatheter fordelivery of the clot engaging element in the collapsed configuration. 9.A clot retrieval system as claimed in claim 8 wherein the lumen of themicrocatheter is configured to receive the tubular shield element.
 10. Aclot retrieval system as claimed in claim 9 wherein the outer diameterof the tubular element is at least as small as the diameter of the clotengagement element in its collapsed configuration.
 11. A clot removaldevice for removing an occlusive clot from a distal blood vessel of apatient, the clot removal device comprising: a clot engaging element, anelongate member and a tractive tubular member, the clot engagementelement having a collapsed delivery configuration and an expandedconfiguration for engaging with the occlusive clot and for dislodgingthe occlusive clot from a distal blood vessel; the elongate membercomprising a proximal section, an intermediate section and a distalsection, a distal end of the distal section of the elongate member beingconnected to the clot engaging element; the elongate member beingconfigured to transmit a pull force to the clot engaging element; thetractive tubular member being configured to encircle the elongate memberover at least a portion of the length of the elongate member distalsection, the distal section of the elongate member being slidable androtatable relative to the tractive tubular member; the elongate memberdistal section and the tractive tubular member being configured tospread tractive forces transmitted by the elongate member.
 12. A clotremoval device as claimed in claim 11 wherein the tractive tubularmember is slidable between a proximal position and a distal positionalong the distal section of the elongate member.
 13. A clot removaldevice as claimed in claim 11 wherein the tractive tubular membercomprises an inner lumen and an outer surface and a proximal abutmentsurface and a distal abutment surface.
 14. A clot removal device asclaimed in claim 11 wherein the interface between the elongate memberdistal end and the tractive tubular member comprises the outer surfaceof the distal section of the elongate member and the inner surface ofthe lumen of the tractive tubular member.
 15. A clot removal device asclaimed in claim 11 wherein the interface between the elongate memberdistal section and the tractive tubular member is configured tofacilitate low friction sliding of the tractive tubular member relativeto the elongate member.
 16. A clot removal device as claimed in claim 14wherein the coefficient of friction of the inner surface of the tractivetubular member is less than the coefficient of friction of the outersurface of the tractive tubular member.
 17. A clot removal device asclaimed in claim 14 wherein the distal section of the elongate membercomprises a polished surface or a buffed surface.
 18. A clot removaldevice as claimed in claim 17 wherein the distal section of the elongatemember comprises a longitudinally polished surface or a longitudinallybuffed surface.
 19. A clot removal device as claimed in claim 11 whereinthe tractive tubular member inner surface comprises a first material andthe tractive tubular member outer surface comprises a second material.20. A clot removal device as claimed in claim 19 wherein the tractivetubular member first material comprises a lower coefficient of frictionthan the tractive tubular member second material.
 21. A clot removaldevice as claimed in claim 11 wherein the elongate member comprises adistal stop and a proximal stop, said distal and proximal stopsconfigured to limit the distance of sliding of the tractive tubularmember.
 22. A clot removal device as claimed in claim 21 wherein theproximal stop and/or the distal stop of the elongate member comprise anabutment surface, a collar, a tube end, a spring end, a tether, atapered shaft section, a diameter change, or a surface projection.
 23. Aclot removal device as claimed in claim 11 wherein elongate member is atleast partially a nitinol material or a stainless steel material.
 24. Aclot removal device as claimed in claim 11 wherein the slider tubeencircles the elongate member distal section over at least a portion ofits length.
 25. A clot removal device as claimed in claim 11 wherein theclot removal device comprises a sliding distance, said sliding distancecomprising the distance along the elongate member that the tractivetubular element can slide without obstruction.
 26. A clot removal deviceas claimed in claim 25 wherein the sliding distance is at least as longas the length of the occlusive clot, the sliding distance may be atleast 10 mm, optionally at least 20 mm, optionally at least 30 mm,optionally at least 40 mm, optionally at least 50 mm, the slidingdistance may be less than 150 mm.
 27. A clot removal device as claimedin claim 11 wherein the clot removal device comprises a microcatheterfor delivery of the clot removal device, the microcatheter comprising alumen sized to receive the clot engagement element in its collapsedconfiguration.
 28. A clot removal device as claimed in claim 27 whereinthe microcatheter lumen is configured to slidably receive the tractivetubular member.
 29. A clot removal device as claimed in claim 11 whereinthe tractive tubular member outer diameter is at least as small as thediameter of the clot engagement element in its collapsed configuration.